[Clang] Restore SafeStack support for x86-32 Fuchsia (#165471)

Fuchsia does not fully support an x86-32 (i?86-fuchsia) target.
But the x86_64-fuchsia target in -m32 mode is used when building
some kernel / boot-loader related code.  This narrow use of an
(effective) i?86-fuchsia target still supports SafeStack using
the same Fuchsia-specific ABI as x86_64-fuchsia.

Author: frobtech

clang/lib/Driver/ToolChains/Fuchsia.cpp

@@ -483,7 +483,8 @@ SanitizerMask Fuchsia::getSupportedSanitizers() const {
   Res |= SanitizerKind::Leak;
   Res |= SanitizerKind::Scudo;
   Res |= SanitizerKind::Thread;
-  if (getTriple().getArch() == llvm::Triple::x86_64) {
+  if (getTriple().getArch() == llvm::Triple::x86_64 ||
+      getTriple().getArch() == llvm::Triple::x86) {
     Res |= SanitizerKind::SafeStack;
   }
   return Res;
@@ -496,6 +497,7 @@ SanitizerMask Fuchsia::getDefaultSanitizers() const {
   case llvm::Triple::riscv64:
     Res |= SanitizerKind::ShadowCallStack;
     break;
+  case llvm::Triple::x86:
   case llvm::Triple::x86_64:
     Res |= SanitizerKind::SafeStack;
     break;

clang/test/Driver/fuchsia.c

@@ -130,6 +130,11 @@
 // RUN:     -resource-dir=%S/Inputs/resource_dir_with_per_target_subdir \
 // RUN:     -fuse-ld=ld \
 // RUN:     | FileCheck %s -check-prefix=CHECK-SAFESTACK
+// RUN: %clang -### %s --target=x86_64-unknown-fuchsia -m32 \
+// RUN:     -fsanitize=safe-stack 2>&1 \
+// RUN:     -resource-dir=%S/Inputs/resource_dir_with_per_target_subdir \
+// RUN:     -fuse-ld=ld \
+// RUN:     | FileCheck %s -check-prefix=CHECK-SAFESTACK
 // CHECK-SAFESTACK: "-resource-dir" "[[RESOURCE_DIR:[^"]+]]"
 // CHECK-SAFESTACK: "-fsanitize=safe-stack"
 // CHECK-SAFESTACK-NOT: "[[RESOURCE_DIR]]{{/|\\\\}}lib{{/|\\\\}}x86_64-unknown-fuchsia{{/|\\\\}}libclang_rt.safestack.a"